Significant Accounting Policies - Impacts on Balance Sheets from the Adoption of ASC 606 (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	$ 159,755		$ 94,930
Accounts receivable, net of allowance	70,408		79,383
Deferred commissions, current	14,543		14,020
Prepaid expenses and other current assets	32,955		21,293
Total current assets	277,661		209,626
Property and equipment, net	39,554
Operating right-of-use asset	24,205
Deferred commissions, net of current portion	28,979		15,088
Deferred tax assets	494		326
Other assets	592		601
Total assets	371,485		233,180
Accounts payable	5,222		9,249
Accrued expenses	7,488		7,464
Accrued compensation and related benefits	10,691		13,796
Deferred revenue, current	82,201		95,523
Operating lease liability, current	3,836
Finance lease liability, current	1,447
Other current liabilities	1,395		2,369
Total current liabilities	112,280		128,401
Operating lease liability, net of current portion	44,416
Finance lease liability, net of current portion	2,375
Deferred revenue, net of current portion	7,139		16,145
Deferred tax liabilities	38		42
Deferred rent, net of current portion	0		15,400
Total liabilities	166,248		159,988
Additional paid-in capital	340,929		218,284
Accumulated other comprehensive (loss) income	(285)		542
Accumulated deficit	(135,413)		(145,640)
Total stockholders’ equity	205,237		73,192	$ 45,524	$ (63,492)
Total liabilities and stockholders’ equity	371,485		233,180
Increase in total deferred commissions	43,522		29,108
Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	3		3
Class B Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	3		$ 3
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	159,755
Accounts receivable, net of allowance	70,408
Deferred commissions, current	20,604
Prepaid expenses and other current assets	16,612
Total current assets	267,379
Property and equipment, net	39,554
Operating right-of-use asset	24,205
Deferred commissions, net of current portion	13,199
Deferred tax assets	494
Other assets	592
Total assets	345,423
Accounts payable	5,222
Accrued expenses	7,488
Accrued compensation and related benefits	10,691
Deferred revenue, current	111,186
Operating lease liability, current	3,836
Finance lease liability, current	1,447
Other current liabilities	1,395
Total current liabilities	141,265
Operating lease liability, net of current portion	44,416
Finance lease liability, net of current portion	2,375
Deferred revenue, net of current portion	12,030
Deferred tax liabilities	38
Deferred rent, net of current portion	0
Total liabilities	200,124
Additional paid-in capital	340,929
Accumulated other comprehensive (loss) income	(605)
Accumulated deficit	(195,031)
Total stockholders’ equity	145,299
Total liabilities and stockholders’ equity	345,423
Calculated under Revenue Guidance in Effect before Topic 606 | Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	3
Calculated under Revenue Guidance in Effect before Topic 606 | Class B Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	3
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit		$ (55,800)
Decrease in total deferred revenue		$ (35,400)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash equivalents	0
Accounts receivable, net of allowance	0
Deferred commissions, current	(6,061)
Prepaid expenses and other current assets	16,343
Total current assets	10,282
Property and equipment, net	0
Operating right-of-use asset	0
Deferred commissions, net of current portion	15,780
Deferred tax assets	0
Other assets	0
Total assets	26,062
Accounts payable	0
Accrued expenses	0
Accrued compensation and related benefits	0
Deferred revenue, current	(28,985)
Operating lease liability, current	0
Finance lease liability, current	0
Other current liabilities	0
Total current liabilities	(28,985)
Operating lease liability, net of current portion	0
Finance lease liability, net of current portion	0
Deferred revenue, net of current portion	(4,891)
Deferred tax liabilities	0
Deferred rent, net of current portion	0
Total liabilities	(33,876)
Additional paid-in capital	0
Accumulated other comprehensive (loss) income	320
Accumulated deficit	59,618
Total stockholders’ equity	59,938
Total liabilities and stockholders’ equity	26,062
Increase in total deferred commissions	9,700
Decrease in total deferred revenue	(33,900)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	0
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Class B Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock	$ 0